We have examined the sleep profile of the Flinders Sensitive Line (FSL) of rats, which were selectively bred for supersensitive responsivity to an acetylcholinesterase inhibitor (DFP). These animals have an increased density of muscarinic receptors in striatum and hippocampus and display a number of behavioral and neuroendocrine characteristics that may represent a rodent analogue of clinical depression. A continuous 48-hour sleep EEG recording was obtained. Compared to control rats (the Flinders Resistant Line), the FSL rats had selectively more rapid-eye-movement (REM) sleep as a percentage of total sleep time. In addition, the REM sleep latency was significantly shorter and the REM-REM cycle length was significantly faster in the FSL than in the FRL strain. The two strains did not differ in total sleep time, drowsy sleep, or slow-wave sleep. The increased REM sleep in the FSL rats is consistent with the amassed evidence that cholinergic mechanisms selectively promote REM sleep, and suggests that the FSL rats may be useful in understanding the mechanism responsible for short REM latency in depression and narcolepsy.